1. Field of the Invention
The present invention relates to wireless communication field, more particularly, relates to method and apparatus for synchronizing card without traffic (i.e. non-traffic card) in multi-card multi-standby mobile terminal.
2. Description of Prior Art
The development of mobile communications provides mobile communication networks of various standard, such as the second-generation mobile communication system (2G): Global System for Mobile Communication (GSM), General Packet Radio System (GPRS), Enhanced Data rates for GSM service (EDGE) and Code Division Multiple Access (CDMA); the third-generation mobile communication system (3G): Universal Mobile Telecommunications System (UMTS, which is also called Wideband CDMA (WCDMA)), Time Division-Synchronous CDMA; and next generation mobile communication system: Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WIMAX).
Different types of wireless network are established in different time. Different wireless networks have different coverage areas. Different network operators provide different services and charge different fees. The development of communication technology is user-centered. Although there is no uniform standard in mobile network technology at present, users have a requirement that different SIM (Subscriber Identity Module) cards can work together in one cell phone, to use different network services from different network operators, which is technically achievable. And another requirement is that one cell phone has two SIM cards in the same network (for example, one SIM card is a local card, and the other is not a local card for business trips and travels).
Therefore, there appeared on market a type of cell phone which has two SIM cards in service. This type of cell phone, which saves money for a second cell phone, is easy to carry and use.
A dual-mode mobile station is disclosed in the US patent application with publication No. 2005/0020286A1. The dual-mode mobile station supports two kinds of mobile communication network, such as GSM, GPRS, CDMA and UMTS, etc. When the dual-mode mobile station receives services from different networks, information will be displayed on a main screen of the mobile station to notify the user the current network; and the user may select phone numbers and services according to the current network.
In addition, a dual-card dual-standby mobile telephone is disclosed in the Chinese patent application with publication No. CN1976516A. The mobile telephone includes a master unit and a slave unit. The master unit includes a host card slot, a host antenna, a host RF module as well as a host baseband processing module; the slave unit includes a slave card slot, a slave antenna, a slave radio frequency (RF) module as well as a slave baseband processing module. By the two sets of antennas, RF modules and baseband processing modules, two SIM cards can be in stand-by status simultaneously.
In a multi-card multi-standby cell phone (such as the above conventional dual-card dual-standby cell phone), when a SIM card (referred to as traffic card SIM-1) is in a voice service (i.e. in traffic), the other SIM card (referred to as non-traffic card SIM-2) which is in standby status may be out of synchronization because of (1) no data being received by the non-traffic card during this time period, (2) user being in a moving status; (3) poor wireless conditions; and (4) weak coverage of a network cell. The out-of-synchronization often causes the non-traffic card SIM-2 to drop from the network, after traffic card SIM-1 finishes the voice service.
Normally, when in idle mode, a cell phone is able to receive and demodulate the broadcast channel (BCH) signal transmitted from the network cell. There is a synchronization channel (SCH) signal in the BCH signal, which is used to adjust time sequence in the cell phone. The out-of-synchronization means that the cell phone is not synchronous with the network cell; working time of the cell phone is not coordinated with working time of the network cell; and the sending and receiving of the signal frame are not synchronous. Because of the out-of-synchronization results, effective signals can not be demodulated and communication can not be established.